feat: add CORS support via CORS_ORIGINS env var

- New CORSMiddleware in server/cors.go
- Reads comma-separated origins from CORS_ORIGINS env
- Empty or "*" allows all origins
- Handles preflight OPTIONS requests
- Wraps existing LoggingMiddleware chain

main.go

@@ -4,6 +4,7 @@ import (
 	"log"
 	"os"
 	"strconv"
+	"strings"
 
 	"AbstractWizard/audit"
 	"AbstractWizard/server"
@@ -11,9 +12,10 @@ import (
 
 func main() {
 	cfg := server.AppConfig{
-		ConfigDir:  envOrDefault("CONFIG_DIR", "/config"),
-		ListenAddr: envOrDefault("LISTEN_ADDR", "127.0.0.1:8080"),
-		MaxBackups: envOrDefaultInt("MAX_BACKUPS", 10),
+		ConfigDir:   envOrDefault("CONFIG_DIR", "/config"),
+		ListenAddr:  envOrDefault("LISTEN_ADDR", "127.0.0.1:8080"),
+		MaxBackups:  envOrDefaultInt("MAX_BACKUPS", 10),
+		CORSOrigins: parseCSV(os.Getenv("CORS_ORIGINS")),
 	}
 
 	if err := os.MkdirAll(cfg.ConfigDir, 0o755); err != nil {
@@ -23,7 +25,8 @@ func main() {
 	auditLog := audit.NewLogger()
 	srv := server.New(cfg, auditLog)
 
-	log.Printf("config_dir=%s listen_addr=%s max_backups=%d", cfg.ConfigDir, cfg.ListenAddr, cfg.MaxBackups)
+	log.Printf("config_dir=%s listen_addr=%s max_backups=%d cors_origins=%v",
+		cfg.ConfigDir, cfg.ListenAddr, cfg.MaxBackups, cfg.CORSOrigins)
 
 	if err := srv.ListenAndServe(); err != nil {
 		log.Fatalf("server error: %v", err)
@@ -49,3 +52,18 @@ func envOrDefaultInt(key string, defaultVal int) int {
 	}
 	return n
 }
+
+func parseCSV(s string) []string {
+	if s == "" {
+		return nil
+	}
+	parts := strings.Split(s, ",")
+	result := make([]string, 0, len(parts))
+	for _, p := range parts {
+		p = strings.TrimSpace(p)
+		if p != "" {
+			result = append(result, p)
+		}
+	}
+	return result
+}